The field of the present invention is screen separators using vibratory motion to enhance separation.
Separation, sifting and the like through screens have long been accomplished with the assistance of vibratory motion. Such motion has been used as a means for vibrating the screens through which material is to pass, thereby using inertia and particle interaction of the material itself in assisting it through the screen, reducing screen blinding effects and physically breaking up clumps of material to improve screening efficiency. Such vibration also can be used as a means for advancing material along a surface. In screening, advancement and screening are both enhanced by vibratory motion. One such screening device is disclosed in U.S. Pat. No. 4,582,597, the disclosure of which is incorporated herein by reference. Also in screening, vibratory motion can be used to cause impacts by the screen with solid elements positioned adjacent the screen for additional cleaning effects. Reference may be made to U.S. Pat. No. 5,051,171, the disclosure of which is incorporated herein by reference.
A plurality of motions have been commonly used for the screening of materials. Round motion may be generated by a simple eccentric located roughly at the center of gravity of a resiliently mounted screening device. Such motion is considered to be excellent for particle separation and excellent for screen life. It requires a very simple mechanism, a single driven eccentric weight. However, round motion acts as a very poor conveyor of material and becomes disadvantageous in continuous feed systems where the oversized material is to be continuously removed from the screen surface. Another common motion is achieved through the counter rotation of adjacent eccentric vibrators also affixed to a resiliently mounted screening structure. Through the orientation of the eccentric vibrators at an angle to the screening plane, linear vibration may be achieved at an angle to the screen plane. Such inclined linear motion has been found to be excellent for purposes of conveying material across the screen surface. However, it has been found to be relatively poor for purposes of separation and is very hard on the screens.
Another motion commonly known is multi-direction elliptical motion wherein the single rotary eccentric vibrator is located at a distance from the center of gravity of the screening device. This generates elliptical motions in the screening device. However, the elliptical motion of any element of the screen has a long axis passing through the axis of the rotary eccentric vibrator. Thus, the motion varies across the screening plane in terms of direction. This motion has been found to produce efficient separation with good screen life. As only one eccentric is employed, the motion is simple to generate. However, such motion is very poor as a conveyor.
In reviewing the motions typically associated with rectangular screening devices, compromises are inevitable. One typically must choose among strengths and weaknesses in conveying capability, screening capability and screen life.